For information on the plethora of known oxo bridged tetranuclear metal compounds, reference is made to the following review articles: K. Wieghardt, Angew. Chem.Int. Ed. English, 28, p. 1153 (1989); J. B. Vincent, G. Christou, Adv. Inorg. Chem., 33, p. 197, (1989); G. Christou, Acc. Chem. Res., 22, p.328 (1989); and G. W. Brudvig, R. H. Crabtree, Prog. Inorg. Chem., 37, p. 99 (1989). These articles describe primarily manganese complexes in which the manganese is present in various oxidation states, spatial arrangements and the like. Other literature references and tetranuclear manganese complexes are referred to and disclosed in U.S. Pat. No. 5,025,101.
Compounds having an oxo (hydroxo) bridged tetranuclear, mixed metal core, however, have not been previously reported. Hence, the ability to prepare such materials is highly desired.
The production of organic hydroperoxides from aryl alkyl hydrocarbons in the presence of various transition metal salt complexes has been described in the literature. See, for example, U.S. Pat. No. 2,954,405 disclosing the production of organic hydroperoxides by autoxidation of hydrocarbons in the presence of molecular oxygen and metal phthalocyanines as catalysts. Similarly, U.S. Pat. No. 4,013,725 discloses a process for preparing hydroperoxides in a homogeneous system by autoxidizing secondary alkyl group-substituted methylbenzenes in the presence of water, a base, an oxygen containing gas, and a water-soluble chelate compound in which multidentate ligands are coordinated to at least one metal from the class of cobalt, nickel, manganese, copper, and iron.
In U.S. Pat. No. 5,025,101 and U.S. Pat. No. 5,183,945 tetranuclear manganese complexes, and their method of preparation, and their use as catalyst in the production of hydroperoxide are disclosed.
In part the present invention is predicated on the discovery that certain compounds having an oxo (hydroxo) bridged tetranuclear, mixed metal core, are useful as oxidation catalysts, in the presence of oxygen containing gas, for the production of organic hydroperoxides.